(1) Field of the Invention
The present invention relates to a method for designing and/or selecting a device and/or a material for implanting in tissues of the human or animal body, and to the device and/or material obtained thereby.
More in particular, the invention relates to a method for designing dental implants and filler materials for the endogenous repair of bone cavities, and extends to dental implants and filler biomaterials obtained thereby.
(2) Description of Related Art
The treatment of certain diseases involves inserting and implanting filler materials or devices inside organs or tissues of the human or animal body. In odontoiatrics, for instance, lost or diseased original teeth can be replaced by prostheses that can be attached to endosseous implants that substitute the missing root. In other fields of surgery, use is made of endosseous fixing screws to fuse vertebrae, or of devices such as stents, which consist of hollow cylindrical mesh elements capable of assuring the patency of biological lumens, such as arteries, veins, bile ducts, oesophagus, colon, trachea, ureter, urethra, etc. In all such cases, the device implanted or inserted in the organ or tissue of interest must subsequently become successfully integrated and stable within the structure and the surrounding tissue.
In the case of endosseous dental implantology, the implant must be stable enough to withstand the masticatory loads, and must consequently enable the onset of a rapid and effective process of osteointegration. The quantity, quality and duration of said osteointegration process depends on the nature of the surface of the implant.
In the case of stents, and of vascular stents in particular, integration with the tissue of the coronary vessels must not only be complete and effective, but must also avoid any excessive growth of neointimal tissue, which can cause restenoses, i.e. re-occlusion of the vessel. This process is also influenced by the nature of the surface of the stent.
Guided bone regeneration (GBR) using filler materials—known in the sector as “biomaterials”—is a technique that has been consolidated by decades of surgical experimentation. These biomaterials are used to regenerate biological tissues, and particularly for bone regeneration in sectors such as orthopaedics, traumatology, spinal surgery, maxillofacial surgery and odontoiatrics.
The pharmaceutical industry and laboratories specialising in biotechnologies have fine-adjusted four basic product categories, i.e. conditioned human bone, conditioned animal bone, natural biomaterials and synthetic biomaterials.
The endogenous repair of bone cavities through endogenous bone formation is a natural physiological event. The animal body is equipped with a complex self-repair system, such that damage to the various body tissues can be repaired, within feasible limits, by means of a reconstruction process. The purpose of all pharmacological processes and surgical procedures implemented on a living organism is to guide the natural physiological processes that lead to healing, or to create the conditions that make healing possible.
A healing process can be facilitated and guided (GBR) by using filler biomaterials that stimulate the natural endogenous formation of new bone tissue. The biomaterials available on the market, be they of natural or synthetic origin, are characterised by a particular morphology that depends on the tissue from which they are derived, or on the substance used to produce them. This morphology is of fundamental importance, so a biomaterial made according to the present method could be better suited to the morphology of the recipient tissue and thus positively influence the response and the healing process of the tissue concerned.
As regards endosseous dental implantology, the patent literature describes various types of implant and methods for their design and manufacture, intended to improve the process of osteointegration and, more in general, to improve the quality and functionality of the implant.
U.S. Pat. No. 5,628,630 (Misch et al.) describes a method for designing skeletal implants in order to optimising the cell response. The implant consists of a screw-in mot and the method for designing the implant entails a macro-design stage and a micro-design stage. The latter involves determining the elastic modulus of the bone, which is then used in a series of strain equations adopted in the design of the implant so as to ensure that the entity of the strains induced by the implant comes between 100 and 3,000 microstrain. The method also includes a classification of trabecular bone in various groups as a function of its density.
The US patent application 2005/0060039 A1 describes a glenoid prosthesis with a serrated surface having a fractal structure to increase its adhesion to the cementing material and consequently to the bone.
The international patent application WO 2007/074498 describes the shape of a screw for an endosseous dental implant. The surface of the interface between the implant and the surrounding bone is—among other things—increased by creating engravings structured according to fractal geometry.
The US patent application 2002/0196966 A1 describes a method and a computer-assisted system for analysing the mass and structure of a bone. The method is based on obtaining digital images of the bone and measuring the bone mineral density and other parameters, including the Minkowski index. Among other things, the method describes the use of fractal analysis to characterise the trabecular structure of a bone.
U.S. Pat. No. 6,430,427 B1 describes a method for obtaining a trabecular index using a model and a trabecular method for estimating bone mineral density. The method analyses variations in the trabecular structure due to decalcification in order to obtain indices that are subsequently used to estimate bone mineral density.
The article by Yi W J, M. Heo, S. Lee, S. Choi, K. Huh, S. Lee; “Direct measurement of trabecular bone anisotropy using directional fractal dimension and principal axes of inertia”; Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology; Volume 104, Issue 1, Pages 110-116, 26 Mar. 2007, describes the directional anisotropy of the fractal structure of trabecular bone and its use to study the mechanical properties of the bone in various regions of the mandible.
Although some of the above-described methods enable useful information to be obtained on the structure of biological organs and tissues destined to receive implants, and particularly of osseous structures, these methods do not enable the design and preparation of implants or devices with a structure morphologically consistent with the biological structure receiving the implant, with a view to achieving a structural complementarity that ensures its effective integration in the recipient structure. Moreover, these known methods are often complicated, so they are not easy to adopt in surgical practice, and in dental practice in particular.